This invention relates to pulse generating apparatus used to feed pulse counters in timers and electrical devices which use manual controls which produce pulses which are counted as the controls are advanced in discrete steps.
Many digital controllers require the system to receive a numerical input from a manually operable rotating shaft or dial. When the input is to be effected by a person rotating a numbered dial, it is necessary that the system receive the exact number of pulses indicated by the markings on the dial. For this purpose, prior art teaches the use of cam operated contacts or printed circuit switches in which a wiper passes over small deposited metallic areas, the number of such areas corresponding to the number of pulses desired in a single rotation of the dial.
It is well known that cam operated contacts and wiping contacts do not produce a single clean "make" and "break" of the electrical circuit, but, instead, produce a series of rapid multiple closures because of bounce or wiper contact noise characteristics. Since digital circuits generally respond faster than the bounce or wiper noise pulses, it is necessary to include "debounce" circuitry so that a series of very rapid pulses will be converted to a single pulse corresponding to a single cam point or contact wiping point. Such debounce circuitry is well known in the art. In digital systems using a synchronizing "clock", the debounce period can easily be chosen to be a multiple of the clock period. Since most system clocks operate at relatively high frequencies their period is short enough that great flexibility is available for choosing the length of the debounce period.
In a manually operable rotary switch of the type described, the rate of rotation is controlled by the user. If a large number of pulses per rotation is desired, the angular rotation between pulses will be small and rapid rotation will cause the pulses to be spaced in time as little as a few milliseconds apart. If the duration of the bounce phenomena exceeds the possible time interval for rotation between switching points, it is obvious that a debounce period long enough to guarantee a single output pulse from each switch point would prevent generating the next desired output pulse. For a cam operated switch, this could require a very careful design of the spring and contact system to minimize the bounce, and very careful control of manufacturing with respect to both materials, assembly methods and testing to assure that the bounce duration did not exceed the maximum specified. Thus, the cost of such a system to assure reliable performance is quite high compared to the switch of this invention.
If a printed circuit type manually operable rotary switch is employed, the cost is considerably greater than the switch of this invention, since the technology of proper circuit metallization and wiper contact performance is quite complex. In addition, the printed circuit switch has a seemingly impossible problem to solve in this application. This problem arises because the switch cannot be made completely noiseless as the wiper moves over the metallic area, especially after some period of use causing wear. Therefore, it is also necessary to include debounce circuitry for printed circuit switches. In this application, the slowest rate of rotation would determine the time duration required for the debounce period. A practical period for the slowest anticipated rotation would greatly exceed the duration of the time interval for the most rapid anticipated rotation, thus precluding the selection of a debounce interval to satisfy the requirement.
In addition to the problems described above, manually operable cam operated contact switches and printed circuit switches suffer from another problem even more difficult to solve. This problem concerns the ability of the user to "tease" the switch by rotating it slightly between detent points or ratchet points; that is, by rotation back and forth far enough to open and close the cam operated contacts or move the wiper on and off the metallic area, but not far enough to engage the next ratchet tooth (which would prevent backward movement) or fall into the next detent position. This results in the possibility that extra pulses are generated between dial marks, thus creating an erroneous numerical input to the system. While various mechanical schemes to avoid this problem could be envisioned, none appear to have the simplicity and low cost of this invention.
An ideal manually operable pulse-producing device for the application described: (1) would, with the use of a simple debouncing circuit, produce a single pulse corresponding to each dial mark as the dial mark is rotated past an index mark; (2) cannot be teased between positions; (3) provides the user with some feedback such as tactile, aural, or both, as each dial mark generates a pulse; and (4) is of simple construction for low cost and reliable performance.
Accordingly, the object of the present invention is to provide a manually operable, electrical pulse-producing apparatus, preferably for the applications described, which have one or more, and preferably all of the desirable features of this ideal switch just described.
The manually operable pulse-producing apparatus of the invention utilizes a pulsing technique heretofore used in the prior art in a different manner and in a different environment than that of the present invention, to produce with each discrete movement of a rotable cam member a series of easy-to-debounce pulses resembling a damped sine wave. Thus, some prior pulse-producing devices utilize the piezo-electric effect of a piezo-electric ceramic element which is initially placed under a relatively small compressive force by a spring to generate electric pulses for energizing lighting or similar devices. Either the spring, or a separate spring-urged arm, engaging the piezo-electric element is positioned along the periphery of a motor driven cam having cam lobes thereon so that the rotation of the cam member will periodically vary the degree of the compression of the piezo-electric element to generate voltage pulses. In one such device, as shown in U.S. Pat. No. 3,174,419, a spring-urged arm rides on a cam and, starting from a point where it is located at a low point on the cam, as the cam is rotated, the arm is moved along a gradually rising side of a cam lobe which gradually increases the stress of a piezo-electric element. An insignificant electrical output is produced at the output terminals of the piezo-electric element during such gradual increase in the stress on the piezo-electric element. Each cam lobe has a steep trailing edge, so that when the spring-urged arm falls suddenly to a low point on the cam, a sudden high amplitude pulse waveform is generated by the piezo-electric element.
In accordance with another feature of the invention, the pulse output of a piezo-electric element operated as described is uniquely used as a pulse source coupled through a debouncing circuit to a circuit responsive to the number of pulses fed thereto, like a pulse responsive circuit of a timer.
In accordance with another feature of my invention, the cam is connected to a manually operable dial knob and the cam forms a ratchet wheel with sawtooth-shaped cam lobes, each defined by a gradually rising leading side terminating in a sharply dropping trailing side. In the most preferred form of my invention, a spring rides on the cam, the spring having a pawl-forming end normally urged into the crotch between successive cam lobes, so that the spring acts as a detent and stops rotation of the ratchet-forming cam in one direction and permits the cam to be rotated in the other direction as the pawl-forming end of the spring rides up along the gradually rising side of a cam lobe. The pawl-forming end of the spring preferably joins a curved portion closely extending part way around a cylindrical pivot-forming rod, where the spring terminates in a flat end bearing against one end of a piezo-electric element to place the element under an initial small degree of compression.
It is thus apparent that the spring, which less desirably can be a spring-urged arm, uniquely forms the double function of both acting as a detent for enabling the discrete advancement of the cam member connected to a rotatable dial knob and as a force-transmitting member to the piezo-electric element.
The dial knob has associated therewith indicia identifying various progressively increasing numbers and/or other markers which are alignable with an index mark at each detented position of the dial knob so that, as the dial knob is advanced from an initial reference point to a selected number or other marker, a corresponding number of pulses are generated at the output of a deboucning circuit coupled to the output of the piezo-electric element.
In accordance with another feature of the invention, to permit the dial knob to be moved into a starting or zero reference position without generating any pulses, the dial knob is made in two pieces, preferably an outer hard grippable knob member which is coupled through a one-way clutch to an inner part which may be the cam shaft, or an inner knob member around which the outer knob member is rotatably mounted, so that the outer knob member may be rotated in one direction to set the dial knob assembly to zero without rotating the cam shaft. When the outer knob member is rotated from said zero position in the opposite operating direction, it will advance the cam shaft to generate one easily debounced pulse train as the outer knob member is moved to the next position.